Phyllosilicate minerals such as kaolinite, talc, chlorite, pyrophyllites and montmorillonite are minerals which contain basic silicates and are used in a variety of applications such as paper manufacturing, talcum powder, tailor's chalk, cosmetics and lubricants. With regards to talc, a slurry of talc is commonly used in paper manufacturing to control, inter alia, pitch and paper coating. To manufacture these slurries, talc is added to water until a suspension having a desired solids content is produced. This process is conventionally referred to as a “makedown” process. Currently available makedown processes yield a talc slurry having about 25-60% solids with a reasonable viscosity.
A large quantity of talc is used in the paper and other industries and reducing the transportation costs of these materials to the customer is the subject of considerable effort. High solids slurries of talc are desirable because they increase the transportation cost effectiveness. However, settling occurs when these higher concentration talc slurries are permitted to stand without agitation as often takes place during shipping and in storage. This results in a thick viscous mass or gel after several days and a dense flocculate at the bottom of the shipping container after longer storage, requiring the customer to employ mechanical devices and considerable effort to redisperse the slurries or to add various chemicals to render the slurries usable. Often, the slurries are returned to the manufacturer as unacceptable.
To overcome these problems, manufacturers and suppliers of phyllosilicate minerals have employed different means of making and shipping mineral slurries to customers. Methods such as shipping in low concentrations, mixing higher concentration slurries with various chemical dispersants, shipping solid ground mineral to regional distribution centers where the slurry is prepared and shipped to nearby customers are all currently employed to deliver a useable mineral slurry product to customers without settling of the product.
U.S. Pat. No. 5,424,259, issued to Yordan et al., discloses a method of making a kaolin clay slurry having at least 50% by weight of kaolin clay by mixing water and a lithium based dispersant and then mixing structured kaolin clay particles with the aqueous composition to form the desired high solids slurry.
U.S. Pat. No. 4,118,246, issued to Horzepa et al., discloses a process for producing kaolin clay slurry having 60% to 70% by weight of kaolin clay using a dispersant and a micromixer. This process requires a use of the special micromixer apparatus.
U.S. Pat. No. 4,144,083, issued to Abercrombie, Jr., provides a method for maintaining the low shear viscosity of a kaolin clay slurry having 60% to 72% by weight of kaolin clay using 0.5 to 3.0 pounds of citric acid or sodium citrate per ton of kaolin clay.
U.S. Pat. No. 4,186,027, issued to Bell et al., discloses a process for making kaolin slurry at a pH from 7.5 to 10.5, having a solids content in the range of from 60% to 75% by weight using a dispersing agent and a water-soluble organic polymer. The slurry is subjected to a particle size separation to reduce the percentage of the particles larger than 10 μm in the slurry to not more than 3% by weight.
U.S. Pat. No. 4,309,222, issued to Hoyt, IV, provides a method for making a kaolin slurry of reduced low shear viscosity in water at a pH of 6 to 8 having a solids content from about 60% to 72% using citrate and polyacrylate.
U.S. Pat. No. 4,650,521, issued to Koppelman et al., provides a process for making a kaolin slurry having a solids content of at least about 65% using a carbonate, a water-soluble organic polyacrylate and a water-soluble anionic phosphate. The slurry is then subjected to a “degritting” process to reduce the percentage of the particles larger than 45 μm in the slurry to not more than 0.2% by weight.
U.S. Pat. No. 4,374,203, issued to Thompson et al., provides a method for making a clay slurry having at least 50% by weight of the clay using anionic and cationic polymers.
In U.S. Pat. No. 6,074,473, issued to Nichols et al., provides a method of using pH adjustment and inorganic salts to disperse talc in a slurry.
However, for various reasons such as limited stability, a need for the use of organic polymers, special mixers and/or a need for particle size separation, the prior art fails to provide an acceptable process for producing low cost, high solids phyllosilicate mineral slurry having desired rheological properties that is sufficiently stable for lengthy storage or long distance transport. Therefore, there is a need for an inexpensive and effective method of preparing a stable phyllosilicate slurry having high solids content.